The $2.5bn of settlements reached in the London interbank offered rate rigging scandal are compelling banks to hand over information in the probe of a separate financial benchmark tied to interest-rate derivatives.

That is, according to a person with knowledge of the matter, who asked not to be identified because details of the investigation aren’t public.

'Those banks have to cooperate at the risk of blowing whatever agreements they have,' Peter Henning, a Wayne State University law professor in Detroit and a former U.S. Justice Department prosecutor, said in a telephone interview. 'They are over a barrel.'

The Justice Department deferred prosecution against the three banks as part of the Libor-rigging settlements and the Commodity Futures Trading Commission, the primary investigator in the ISDAfix probe, will keep it 'apprised of what’s going on,' Henning said. Barclays has turned over recorded telephone calls of its traders to the CFTC, Bloomberg News reported last week.